As shown in FIG. 1, a vacuum evaporation device in the prior art includes an evaporation chamber 5 and a base plate 1 located at the lower part of the evaporation chamber 5. A substrate 4 to be evaporated is placed at the upper part of the evaporation chamber 5. An evaporation source device 10 is provided at the edge part of the base plate 1. A baffle 3 is provided at the middle part of the evaporation chamber 5. A baffle opening 31 is formed in the baffle 3, and the position of the baffle opening 31 corresponds to the position of the evaporation source device 10. During evaporation, the evaporation substance evaporated out from the evaporation source device 10 is deposited on the surface of the substrate 4 through the baffle opening 31.
As shown in FIG. 2, each baffle opening 31 is provided with a baffle opening cover plate 32 capable of moving (or rotating) and covering the baffle opening 31. The baffle opening cover plate 32 is used for occluding the baffle opening 31 when the evaporation source device 10 is at a preheated state, so that the evaporation substance evaporated out from the evaporation source device 10 is prevented from polluting the inner surface of the evaporation chamber 5.
However, as the baffle opening 31 is provided at the edge part of the base plate 1, in accordance with the molecular diffusion free-path principle, this will result in non-uniform thickness distribution of a coating film deposited on the surface of the substrate 4, and the thickness of the coating film near the evaporation source device 10 is far greater than that of the coating film away from the evaporation source device.